Naturally, body membranes of all sorts represent protective barriers against foreign materials and infection. However, administration of drugs using transdermal and trans-membrane delivery systems does provide improved therapeutic advantages and better patient compliances which is well known and documented in both the patent and scientific literature. Examples of such systems are disclosed in U.S. Pat. Nos. 3,921,636; 3,964,482; 3,989,816; 3,996,934; 4,201,211; 4,291,014; 4,291,015; 4,292,203; 4,336,243; 4,346,709; 4,379,454; 4,409,206; 4,460,372; 4,486,193; and 4,490,322.
Administration using transdermal and trans-membrane drug delivery systems has certain advantages over the conventional methods of oral and systemic administration. These advantages include: (1) minimizing drug exposure by allowing a significant reduction in dosage; (2) providing long-term therapy in a single dose thereby increasing patient compliance; (3) avoiding the risks and inconveniences of intravenous or intramuscular therapy; (4) rendering possible the use of drugs with short biological half-lives; (5) allowing immediate termination of drug input by simply removing the material containing the drug; and (6) avoiding the possible inactivation of a drug when it first passes through the liver after oral administration.
Examples of drugs which have been administered transdermally include scopolamine, nitroglycerine, clonidine, estradiol, antibiotics (e.g., erythromycin, lincomycin, and the like), antifungal agents, and sunscreens. Many of these drugs, e.g., clonidine, scopolamine, and nitroglycerine are of such chemical structure that they can permeate the skin and other body membranes to provide sufficiently high therapeutic doses for most purposes. However, when higher therapeutic levels are required, or when the drug itself, e.g., estradiol diacetate, does not permeate or cannot sufficiently permeate the skin to provide the desired level of drug concentration, it becomes necessary to use adjuvants which enhance the rate of penetration of the drug. Generally, for transdermal formulation of most drug entities adjuvants are required.